1. Field of the Invention
The present invention relates to a servo track writing device for recording a format pattern including a servo frame in a magnetic disc drive unit and a method thereof and more particularly to a servo track writing device for recording a format pattern including a servo frame by generating a clock signal from a disc scale by means of a non-contact sensor and a method thereof.
2. Description of the Related Arts
When a servo frame pattern is recorded into a magnetic disc of a hard disc drive using a device conventionally known as a servo track writer (STW) at the manufacturing stage, a reference clock is necessary for achieving synchronism between a write position in the circumferential direction on a disc medium plane and a write signal.
According to an ordinary method, the clock signal is written directly into the disc medium using a reference head which is a specialized magnetic head and then, the reference clock is generated by reading this signal for reference.
According to this method, an assembled disc enclosure case needs to have a hole for inserting the reference head and thus, a servo frame signal must be written in a clean room for dust protection.
Further, because the reference head needs to be often replaced because of its consumption, it has a problem of low production efficiency. To solve these problems, a device which generates a clock using a non-contact sensor is considered.
However, when a clock is generated using the non-contact sensor, the frequency of the reference clock is fixed by the revolution numbers of an encoder bonded to a disc face as a seal and the disc. Consequently, even if circuit processing for ordinary frequency conversion is carried out, nothing but a clock which is produced by multiplication by an integer or dividing by an integer of the reference clock can be obtained and therefore, there is such an inconvenience that an arbitrary clock frequency (format frequency) required for writing of the servo frame pattern cannot be set up freely.
Further, the clock itself changes due to unevenness of the density of the clock pattern formed on the encoder scale, a deflection of the rotation of a disc or the like. Further, when the disc enclosure is vibrated a clock jitter occurs. Consequently, physical sector starting positions on a disc face can deflect in the radius direction and therefore, there is such a problem that the time of each sector also deflects more largely as compared to a case where there is no rotation deflection or vibration.